www.desatech.com
105163-01C
6
Unusually tight construction is defined as
construction where:
a. walls and ceilings exposed to the out-
side atmosphere have a continuous
water vapor retarder with a rating of
one perm (6 x 10
-11
kg per pa-sec-m
2
) or
less with openings gasketed or sealed
and
b. weather stripping has been added on
openable windows and doors and
c. caulking or sealants are applied to
areas such as joints around window
and door frames, between sole plates
and floors, between wall-ceiling joints,
between wall panels, at penetrations
for plumbing, electrical and gas lines
and at other openings.
If your home meets all of the three criteria
above, you must provide additional fresh
air. See
Ventilation Air From Outdoors
,
page 7.
If your home does not meet all of the three
criteria above, proceed to
Determining
Fresh-Air Flow for Firebox Location
.
Confined and Unconfined Space
The
National Fuel Gas Code ANS Z223.1/NFPA
54
defines a confined space as a space whose
volume is less than 50 cubic feet per 1,000 Btu
per hour (4.8 m
3
per kw) of the aggregate input
rating of all appliances installed in that space and
an unconfined space as a space whose volume is
not less than 50 cubic feet per 1,000 Btu per hour
(4.8 m
3
per kw) of the aggregate input rating of
all appliances installed in that space. Rooms com-
municating directly with the space in which the
appliances are installed*, through openings not
furnished with doors, are considered a part of the
unconfined space.
This heater shall not be installed in a confined
space or unusually tight construction unless provi-
sions are provided for adequate combustion and
ventilation air.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation grills
between them.
aiR FOR COMBUSTiON
aND VENTiLaTiON
Continued
DETERMINING FRESH-AIR FLOW
FOR FIREBOx LOCATION
Determining if You Have a Confined or
Unconfined Space
Use this work sheet to determine if you have a
confined or unconfined space.
Space:
Includes the room in which you will install
heater plus any adjoining rooms with doorless
passageways or ventilation grills between the
rooms.
1. Determine the volume of the space (length x
width x height).
Length x Width x Height =__________cu. ft.
(volume of space)
Example:
Space size 22 ft. (length) x 18 ft.
(width) x 8 ft. (ceiling height) = 3168 cu. ft.
(volume of space)
If additional ventilation to adjoining room is
supplied with grills or openings, add the volume
of these rooms to the total volume of the space.
2. Multiply the space volume by 20 to determine
the maximum Btu/Hr the space can support.
__________ (volume of space) x 20 = (Maxi
-
mum Btu/Hr the space can support)
Example:
3168 cu. ft. (volume of space) x 20 =
63,360 (maximum Btu/Hr the space can support)
3. Add the Btu/Hr of all fuel burning appliances in
the space.
Gas water heater*
_____________Btu/Hr
Gas furnace
_____________Btu/Hr
Vented gas heater
_____________Btu/Hr
Gas fireplace logs
_____________Btu/Hr
Other gas appliances* +
____________Btu/Hr
Total
= ____________Btu/Hr
* Do not include direct-vent gas appliances. Di-
rect-vent draws combustion air from the outdoors
and vents to the outdoors.
Example:
Gas water heater
_____________Btu/Hr
Gas firebox logs
+ ____________Btu/Hr
Total
= ____________Btu/Hr
4. Compare the maximum Btu/Hr the space can
support with the actual amount of Btu/Hr used.
_________Btu/Hr (maximum the space can support)
_________Btu/Hr (actual amount of Btu/Hr used)
Example:
63,360 Btu/Hr (maximum the space
can support)
79,000 Btu/Hr (actual amount of
Btu/Hr used)
40,000
39,000
79,000